json-c d'accord library (libjsoncdac)

jsonc-daccord is a JSON Schema validation library written in C, and is taking advantage of the json-c library.

Design Goals

The goal is to have a lightweight JSON Schema validation implementation in C using json-c. json-c is popular in OpenWRT communities.

Many of the schema features are made optional, and can be disabled if not needed.

Supported schema keywords:

object type	feature
all	type, enum, required, properties, const
object	dependentRequired, propertyNames, patternProperties, additionalProperties
string	minLength, maxLength
numbers	minimum, maximum, multipleOf, exclusiveMinimum, exclusiveMaximum
boolean	additionalProperties
array	minItems, maxItems, uniqeItems, items

Other: $defs, $ref

Example Use

Public headers:

See jsoncdaccord.h

    int jdac_validate_file(const char *jsonfile, const char *jsonschemafile);
    int jdac_validate(json_object *jobj, json_object *jschema);
    int jdac_ref_set_localpath(const char *_localpath);

    const char* jdac_errorstr(unsigned int jdac_errors);

Link your binary to: -ljsoncdac -ljson-c

Use the #include header: #include <jsoncdaccord.h>

Example C code:

#include <stdio.h>
#include <json-c/json.h>
#include <jsoncdaccord.h>

int main(int argc, char *argv[])
{
    char *json_file = "test.json";
    char *schema_file = "schema.json";

    // optional: load referenced schema files from filesystem
    char *localpath = "/my/path/to_json_files/";
    jdac_ref_set_localpath(localpath);

    printf("validating %s with %s\n", json_file, schema_file);
    int err = jdac_validate_file(json_file, schema_file);
    if (err==JDAC_ERR_VALID) {
        printf("validation ok\n");
    } else {
        printf("validate failed %d: %s\n", err, jdac_errorstr(err));
    }
    return err;
}

See jdac-cli.c as well.

Install

Building from source:

Install json-c and libcmocka-dev (used in the debug builds).

• Release version:

git clone --branch libjsoncdac-0.3 https://github.com/domoslabs/jsonc-daccord &&\
cd jsonc-daccord && mkdir build && cd build &&\
cmake .. -DCMAKE_BUILD_TYPE=Release && make && sudo make install

• Debug version:

git clone --branch libjsoncdac-0.3 https://github.com/domoslabs/jsonc-daccord &&\
cd jsonc-daccord && mkdir build && cd build &&\
cmake .. -DCMAKE_BUILD_TYPE=Debug && make && sudo make install

Note: After install you might need to run sudo ldconfig.

CMake Options

build options:

option	description
CMAKE_BUILD_TYPE	Build as Release or Debug. Default: Release.
JDAC_RUN_TESTS	jdac unit tests (CMAKE_BUILD_TYPE=Debug Only)
JDAC_RUN_TEST_SUITE	Run json-schema-org's JSON-Schema-Test-Suite
JDAC_USE_ASAN	Build with address sanitizer
JDAC_STATIC_ANALYZER	Build with static analyzer
JDAC_SHARED_LIBS	Build .so file, .a otherwise
JDAC_BUILD_ALL	override build options below and build all
JDAC_BUILD_ERROR_OUTPUT	Show failing validations with neat error messages
JDAC_BUILD_PATTERN	Support pattern.
JDAC_BUILD_PATTERNPROPERTIES	Support patternProperties
JDAC_BUILD_ADDITIONALPROPERTIES	Support additionalProperties
JDAC_BUILD_PROPERTYNAMES	Support propertyNames
JDAC_BUILD_SUBSCHEMALOGIC	Support allOf, anyOf, oneOf, not, if-then-else
JDAC_BUILD_CONTAINS	Support contains, minContains, and maxContains
JDAC_BUILD_DOWNLOAD	Support downloading referenced schema files
JDAC_BUILD_STORE	Support build a list of schema uri, id, and anchors
JDAC_BUILD_REF	Support $ref keyword. load schemas by file.

Note: Some build options may be off by default. Like DOWNLOAD. Not everyone needs curl+crypto on their system for this.

Run tests

This should be done before each test For debug builds:

mkdir build
cd build && \
cmake .. -DJDAC_BUILD_ALL=ON -DJDAC_RUN_TESTS=ON -DCMAKE_BUILD_TYPE=debug -DJDAC_USE_ASAN=ON && \
make

ctest
ctest -V # to see output of tests
ctest -R dep -V # to test only output test-dependent

To run the test suites, set RUN_TEST_SUITE=ON in the cmake options.

Command Line Interface

You can try the library with the jdac-cli command.

jdac-cli -h

Running clang-tidy

Build with the export compile commands flag then run clang-tidy

mkdir build
cd build
cmake .. -DCMAKE_EXPORT_COMPILE_COMMANDS=1
make
cd ..
run-clang-tidy -p ./build/

To do

• prevent infinite recursion

Related links

• https://json-schema.org/specification.html
• https://github.com/json-schema-org/JSON-Schema-Test-Suite
• https://github.com/json-c/json-c